FLIGHT JANUARY 2ND.. 1947
Naval Aircraft
Design Requirements Discussed by Supermarine Technical Staff
LECTURING before the Southamp-ton Branch of the Royal Aero-' nautical Society on December
nth, Mr. A. N. Clifton, M.B.E.,
B.Sc, F.R.Ae.S., chief of Vickers-
Armstrongs (Supermarine) Technical
Office, outlined the development of
naval aircraft and explained some-
thing of the technical requirements in
modern machines for naval use.
Naval aircraft design, he said, was
really ordinary aircraft design made
more difficult. The first handicap was
the severity of take-off requirements.
Although a certain amount of wind
due to the ship's speed could be relied
upon, long runs were out of the ques-
tion and catapult spools and accelera-
tor hooks must be provided and the
aircraft must have the necessary
strength to withstand the added forces
imposed. Provision for rocket accelera -
ting gear must also be made. Control
characteristics and view must be
specially studied and undercarriage
shock absorption and rebound damp-
ing of a high order were necessary. An
arrester hook and an airframe suitably
strengthened for this attachment were
other requirements. Radio equipment
for naval use was more complicated
and heavier than that required on
landplanes and provision for wing fold-
ing and restrictions on dimensions were
necessary.
To indicate the increase in weight
necessary, Mr. Clifton gave an esti-
mate for a fighter, showing that the
additional weight for a machine of
approximately io,ooolb was at least
45olb made up as follows: —
Accelerator books and pro-vision for KATOG 5olb.
Arrester hook 6olb.
Extra radio 3olb.
Folding wings, slinging and
lashing points iGolb.
Longer stroke undercarriage. . 401b.
Provision for oil heating, fuel
draining, etc 5lb.
345'u-E-'xtra structure weight at 3c
per cent / 1051b.
TOTAL INCREASE /. 4501b.
Landing are^of an air-craft carrier and an
airfield runway compared.
LANDING AREA
A/C CARRIER 2OPFSJ
DECK
AIRFIELD RUNWAY
I5OOYDS-
Examining the take-off question in
detail, Mr. Clifton dealt first with the
normal take-off, using engine -power
alone. Bearing in mind that more
than half the deck might be required
for aircraft landing on, he said, this
was only possible under favourable
conditions. Partially lowered flaps
were essential and a contra-rotating
airscrew, which eliminated swing, was
desirable.
Under less favourable conditions
rockets could be used for acceleration.
These were carried in jettisonable con-
tainers and delivered their thrust ap-
proximately through the C.G. in side
elevation. The standard rocket gave
a thrust of i,2oolb for four seconds and
weighed 661b, and a container for two
rockets weighed 5olb. Four rockets
might be carried on a fighter to attain
a 500-ft run in still air, or a 250-ft run
against a 20-knot wind. This worked
out at an average acceleration of about
1 G, of which I G might be provided
by the engine. /
Finally there was the accelerator, a
2000
woo
10 20 30
DEFLECTION OF FLAP- DEGREES
40
Variation of take-off distance with flapdeflection. (Naval fighter with 47-5 lb/
sq ft wing loading.)
mechanical device. The British type
consisted of a trolley which was rather
similar to the naval catapult in that it
engaged four spools on the airframe.
The forward attachments supplied the
thrust and floated vertically while the
rear ones held up the tail. The trolley
was hauled by a rope running below
a slot in the deck and the motive
power was compressed air or cordite.
With a maximum acceleration of about
2| G (or a mean acceleration of if G)
plus airscrew thrust over a distance of
100 ft the speed at the end was about
60 knots, relative to the ship. To this
speed could be added an allowance of
20 knots for the wind speed over the
deck, giving a total airspeed of 80
knots.
A simpler method was developed by
the U.S. Navy and had since been
250
' 2<3 CONTRA ROTATING
AIRSCREW PLUS
4 ROCKETS
2x3 CONTRA-ROTATING
AIRSCREW PLUS 1_
2)S?ACCELERAT0R
\
0 5 10 15 20 25 30
THRUST (1000 POUNDS)
Variation of take-off distance in 27knot wind with thrust. (Naval fighter
with wing loading of 47-5 lb/sq ft.Take-off power 1,900 b.h.p.
adopted here. This generally used two
hooks on the aircraft with a strap to
engage these, and a claw projecting
through a slot in the deck and pro-
pelled by the accelerating mechanism.
The aircraft ran on its own main and
tail wheels and at the end of the run
the cable was left behind and fell off
the hooks. The loads on the under-
carriage were fairly severe though
generally speaking not severe enough
to call for increased strength. These
loads were due to the downward slope
of the cable, and resulted in the
machine running along on nearly flat
tyres, The cable direction was care-
fully selected to pass just below the
C.G. to avoid nosing over and too
great a tail-wheel load. The advan-
tages of this method were a minimum
of gear above deck, quickness in opera-
tion (because no trolleys had to be
lined up and engaged) and simpler and
lighter attachments on the aircraft.
Launching' Rate
An essential requirement for take-
off was a high rate of launching. For
one thing the aircraft might be wanted t.,
in a hurry, and secondly the carrier . |
might have to lose station relativist"-
accompanying ships due to the neces-
sity to steam into wind. Under favour-
able conditions, a squadron of twelve
aircraft could be launched by accelera-
tion in about 10 minutes. In that
time the remainder of the Fleet might
be 7 or 8 miles ahead.
Landing-on was a different matter
altogether. It was a hazardous pro-
cess calling for a high degree of co-
ordinated skill on the part of the pilot
and the " batsman " directing him. In
the air perfect control was essential,
and once on the deck the aircraft must
not bounce. la the latter respect aero-